Abstract: AIM: To determine the influence of remifentanil on effect site concentration of propofol for loss of consciousness. METHODS: Patients scheduled for general anesthesia were randomly enrolled into group RP and group P. Group RP received target controlled infusion of remifentanil until an effect site concentration of 4 ng/mL was achieved. Then propofol was infused with a target plasma concentration of 4 μg/mL. Group P received infusion of propofol of the same target concentration. The effect site concentration of propofol for the patient losing consciousness was recorded.RESULTS: For the group RP, the ECe₅₀ of propofol effect site concentration for patients losing consciousness was 0.84(0.75,0.93) μg/mL,while the ECe₉₅ value was 1.40(1.27,1.59) μg/mL. However, for the group P, the ECe₅₀ value was 1.9(1.83,1.98) μg/mL and the ECe₉₅ value was 2.8(2.72,2.94) μg/mL. There were significant differences between the two groups considering both the two values (both P<0.05). Time to LOC and propofol needed to LOC was significantly lower in the RP group, while Narcotrend index was higher. Furthermore, the decrease of MAP was more significant in the RP group (all P<0.05).CONCLUSION: Remifentanil could increase the sedative effect of propofol and decrease the effect site concentration of propofol for loss of consciousness.

Key words: remifentanil, propofol, target controlled infusion, loss of consciousness, effect site concentration